Thin film resistor having surface mounted trimming bridges for incrementally tuning resistance

ABSTRACT

A resistor assembly is disclosed and comprises a first conductive trace, a second conductive trace, and a plurality of trimming bridges that electrically couple the first conductive trace to the second conductive trace. The resistor assembly also comprises a thin film resistor electrically coupled to the first conductive trace. The first conductive trace, the second conductive trace, the plurality of trimming bridges, and the thin film resistor are all part of a surface mounted layer of the resistor assembly. The plurality of trimming bridges are each removable to increase a resistance of the thin film resistor.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/559,066 filed on Sep. 3, 2019. The entirety of this priorityapplication is hereby incorporated by reference.

INTRODUCTION

The present disclosure relates to a thin film resistor. Moreparticularly, the present disclosure relates to a surface mounted thinfilm resistor having a plurality of trimming bridges, where eachtrimming bridge is removable to incrementally tune a resistance of thethin film resistor.

BACKGROUND

Thin film resistors are typically created by depositing a thin filmconstructed of a metal alloy upon a substrate. Specifically, the thinfilm is deposited upon a substrate using a sputtering depositionprocess. Thin film resistors are found in laminate substrates used forelectronic applications such as, for example, printed circuit boards.

A thin film resistor may be attached to a top surface of the electronicsubstrate or, alternatively, embedded within the laminate substrate.When embedded in a substrate, the thin film resistor is referred to asan embedded thin film resistor. Embedded thin film resistors aretypically composed of nickel-chromium alloys such as, for example,nickel chromium aluminum silicon (NiCrAlSi). The nickel-chromium alloyis deposited upon a copper foil. The nickel-chromium alloy and thecopper foil are then bonded to a dielectric layer using a laminationprocess, where the copper foil acts as a conductive layer and thenickel-chromium alloy acts as a resistive layer. The resistive layer isthen etched to define discrete embedded thin film resistors. Any numberof etching process may be used to define the embedded thin filmresistors, however, the specific etching process is selected based onthe specific metals included in the nickel-chromium alloy.

The resistance variation of a thin film resistor depends upon severalfactors. Specifically, physical properties such as, for example, filmthickness, residual stress, uniformity, and surface roughness of theconductive layer may affect the resistance variation of the thin filmresistor. Moreover, the sheet resistance of the nickel-chromium alloybefore etching is inversely proportional to thickness. The thickness ofthe nickel-chromium layer is determined based on sputtering parameterssuch as linear speed and power, however, the sputtering parameters maybe difficult to control. Additionally, the resolution and specific typeof etching used to create the discrete resistor elements also affectsthe resistance variations. Finally, the temperature and cycle time ofthe lamination process also affects the resistance of thenickel-chromium alloy. Thus, it is challenging to control the resistancevariation of a thin film resistor.

SUMMARY

According to several aspects, a resistor assembly is disclosed. Theresistor assembly comprises a first conductive trace, a secondconductive trace, and a plurality of trimming bridges that electricallycouple the first conductive trace to the second conductive trace. Theresistor assembly also comprises a thin film resistor electricallycoupled to the first conductive trace. The first conductive trace, thesecond conductive trace, the plurality of trimming bridges, and the thinfilm resistor are all part of a surface mounted layer of the resistorassembly. The plurality of trimming bridges are each removable toincrease a resistance of the thin film resistor.

In another aspect, a multilayer substrate is disclosed. The multilayersubstrate comprises an uppermost layer defining an uppermost surface ofthe multilayer substrate. The multilayer substrate also comprises asurface mounted layer disposed along the uppermost layer of the of themultilayer substrate. The surface mounted layer of the resistor assemblycomprises a first conductive trace, a second conductive trace, and aplurality of trimming bridges that electrically couple the firstconductive trace to the second conductive trace. The surface mountedlayer of the resistor assembly also comprises a thin film resistorelectrically coupled to the first conductive trace, where the pluralityof trimming bridges are each removable to increase a resistance of thethin film resistor.

In still another aspect, a system for determining resistance isdisclosed. The system comprises a resistor assembly comprising a surfacemounted layer. The surface mounted layer of the resistor assemblycomprises a first conductive trace, a second conductive trace, and aplurality of first trimming bridges that electrically couple the firstconductive trace to the second conductive trace. The surface mountedlayer of the resistor assembly further comprises a third conductivetrace, a fourth conductive trace, and a plurality of second trimmingbridges that electrically couple the third conductive trace to thefourth conductive trace. The surface mounted layer of the resistorassembly further comprises a thin film resistor electrically coupled tothe first conductive trace and the third conductive trace. The pluralityof first trimming bridges and the plurality of second trimming bridgesare each removable to increase a resistance of the thin film resistor.The surface mounted layer of the resistor assembly also comprises firstprobing location disposed on an end of the second conductive trace and asecond probing location disposed on an end of the third conductivetrace. The system further comprises a probe configured to measure afirst current measurement and a first voltage measurement at the firstprobing location and a second current measurement and a second voltagemeasurement at the second probing location. The first currentmeasurement, the first voltage measurement, the second currentmeasurement, and the second voltage measurement determine the resistanceof the resistor assembly.

The features, functions, and advantages that have been discussed may beachieved independently in various embodiments or may be combined inother embodiments further details of which can be seen with reference tothe following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 is a cross-sectioned view of a multilayer substrate comprising aresistor assembly, according to an exemplary embodiment;

FIG. 2 is a top view of the multilayer substrate shown in FIG. 1 where asurface mounted layer of the resistor assembly is visible, according toan exemplary embodiment;

FIG. 3 is an elevated perspective view of the resistor assembly shown inFIG. 1 comprising an embedded thin film resistor and the surface mountedlayer, according to an exemplary embodiment;

FIG. 4A illustrates another embodiment of the surface mounted layershown in FIG. 2, according to an exemplary embodiment;

FIG. 4B is an alternative embodiment of the surface mounted layer seenin FIG. 4A, where the surface mounted layer is asymmetrical, accordingto an exemplary embodiment;

FIG. 5 is a perspective view of the resistor assembly shown in FIG. 4A,according to an exemplary embodiment;

FIGS. 6A-6E illustrate the trimming bridges of the surface mounted layerof the disclosed resistor assembly being trimmed incrementally to tune aresistance, according to an exemplary embodiment;

FIG. 7 illustrates an exemplary four-point probe for measuring voltageand current of the surface mounted layer seen in FIGS. 6A-6E, accordingto an exemplary embodiment;

FIG. 8 illustrates locations for measuring the voltage and current onthe surface mounted layer, according to an exemplary embodiment;

FIG. 9 is a process flow diagram illustrating a method for tuning theresistance of the resistor assembly using the four-point probe shown inFIG. 7, according to an exemplary embodiment; and

FIG. 10 is a top view of an alternative embodiment of the resistorassembly comprising a surface mounted thin film resistor, according toan exemplary embodiment.

DETAILED DESCRIPTION

A resistor assembly is disclosed. The resistor assembly comprises a thinfilm resistor electrically coupled to a surface mounted layer. Thesurface mounted layer of the resistor assembly is disposed along anuppermost layer of a multilayer substrate, and comprises of at least afirst conductive trace, a second conductive trace, and a plurality oftrimming bridges that electrically couple the first conductive trace tothe second conductive trace. In one approach, the thin film resistor isan embedded thin film resistor, however, in an alternative approach thethin film resistor is a surface mounted component disposed along theuppermost surface of the multilayer substrate. The resistance of thethin film resistor is fine-tuned by incrementally removing the trimmingbridges to achieve a defined resistance criterion. Accordingly, themethod of fine tuning the resistance of the thin film resistor isindependent of the processes used to fabricate the thin film resistorand the multilayer substrate.

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses.

Referring to FIG. 1, an exemplary multilayer substrate 10 is shown. Themultilayer substrate 10 comprises three or more dielectric layers 12 anda resistor assembly 20. Specifically, the multilayer substrate 10comprises of an uppermost layer 14 and a plurality of lower layers 16that are disposed underneath the uppermost layer 14. In the embodimentas shown, the lower layers 16 comprise of one middle layer 18A and acarrier layer that is referred to as a bottommost layer 18B. Althoughonly one middle layer 18A is shown, in an alternative approach the lowerlayers 16 comprise of more than one middle layer 18A. The bottommostlayer 18B defines a lowermost surface 22 of the multilayer substrate 10.A plurality of solder balls 27 are disposed along the lowermost surface22 of the multilayer substrate 10.

The resistor assembly 20 comprises a surface mounted layer 24 and asecond layer 26. The second layer 26 of the resistor assembly 20 isdisposed underneath the surface mounted layer 24 and comprises anembedded thin film resistor 28. The surface mounted layer 24 of theresistor assembly 20 is disposed along an uppermost surface 30 of themultilayer substrate 10 and is positioned within the uppermost layer 14of the multilayer substrate 10. In the embodiment as shown in FIG. 1,the second layer 26 of the resistor assembly 20 is disposed within themiddle layer 18A of the multilayer substrate 10. In an embodiment, ifthe multilayer substrate 10 comprises more than one middle layer 18A,then the thin film resistor 28 is disposed within any of the middlelayers 18A. In one non-limiting embodiment, the embedded thin filmresistor 28 is constructed of a nickel-chromium alloy such as, but notlimited to, nickel chromium aluminum silicon (NiCrAlSi). However, it isto be appreciated that the embedded thin film resistor 28 may beconstructed of other resistive alloys as well.

FIG. 2 is a top view of the uppermost surface 30 of the multilayersubstrate 10 shown in FIG. 1, where the surface mounted layer 24 of theresistor assembly 20 is visible. The embedded thin film resistor 28 isnot visible in FIG. 2, as the embedded thin film resistor 28 is disposedwithin the middle layer 18A of the multilayer substrate 10 (seen in FIG.1). Although FIGS. 1, 2, and 3 illustrate an embedded thin film resistor28, in an alternative approach seen in FIG. 10 the resistor assembly 20comprises a surface mounted thin film resistor 428 that is not embeddedwithin the multilayer substrate 10. Instead, the thin film resistor 428is disposed along the uppermost surface 30 of the multilayer substrate10. The thin film resistor 428 is described below.

Referring back to FIG. 2, the surface mounted layer 24 comprises a firstconductive section 36. Although FIG. 2 illustrates the surface mountedlayer 24 comprising of only the first conductive section 36, in theembodiments shown in FIGS. 4A, 4B, and 5, the surface mounted layer 24also comprises a second conductive section 38 as well, which isdescribed below. Referring to FIG. 2, the first conductive section 36 ofthe surface mounted layer 24 comprises a first conductive trace 40, asecond conductive trace 42, and a plurality of trimming bridges 44 thatelectrically couple the first conductive trace 40 to the secondconductive trace 42. As explained below, the plurality of trimmingbridges 44 are each removeable to incrementally adjust a resistance ofthe embedded thin film resistor 28.

Although FIG. 2 illustrates five trimming bridges 44 electricallycoupling the first conductive trace 40 to the second conductive trace42, the surface mounted layer 24 may comprise any number of multipletrimming bridges 44. It is to be appreciated that increasing the numberof trimming bridges 44 results in the ability to adjust the resistanceof the embedded thin film resistor 28 with greater precision. Thesurface mounted layer 24 of the resistor assembly 20 is constructed of aconductive alloy such as, but not limited to, copper or aluminum. FIG. 2also illustrates the plurality of trimming bridges 44 spaced at equaldistances D from one another, where spacing the trimming bridges 44 atequal distances D from one another result in a linear increase in theresistance of the embedded thin film resistor 28 as each trimming bridge44 is removed. In another embodiment, the trimming bridges 44 are spacedat unequal distances from one another. However, it is to be appreciatedthat spacing the trimming bridges 44 at unequal distances from oneanother results in a non-linear increase in resistance between eachtrimming bridge 44.

In the embodiment as shown, the second conductive trace 42 is positionedradially outward relative to the first conductive trace 40. The firstconductive trace 40 and the second conductive trace 42 are arrangedconcentrically with respect to one another relative to a common centralaxis 46. The first conductive trace 40 and the second conductive trace42 are both comprised of a plurality of segments 48 that are arranged inan arcuate profile. Therefore, the first conductive trace 40 and thesecond conductive trace 42 both comprise an arcuate profile. Although anarcuate profile is illustrated in the figures, it is to be appreciatedthat the first conductive trace 40 and the second conductive trace 42are not limited to the profile as shown in the figures and may compriseof other profiles shaped as open polygons. For example, in anotherembodiment, the first conductive trace 40 and the second conductivetrace 42 are shaped as an open pentagon, where the fifth line segment ofthe pentagon is omitted. However, it is to be appreciated the arcuateprofile as seen in FIG. 2 is more compact and requires less space alongthe uppermost surface 30 of the multilayer substrate 10 when compared tosome alternative profiles.

The first conductive trace 40 and the second conductive trace 42 bothhave the same width W. Furthermore, the first conductive trace 40 andthe second conductive trace 42 have a constant width W along theirrespective lengths L. It is to be appreciated that the equal distances Dbetween the trimming bridges 44, the constant width W of the conductivetraces 40, 42, and the arcuate profile of the conductive traces 40, 42all result in a linear difference in resistance as the trimming bridges44 are incrementally removed. Thus, as explained below and as seen inFIGS. 6A-6E, when the trimming bridges 44 are removed, this results in alinear increase in resistance of the resistor assembly 20.

FIG. 3 is a perspective view of the resistor assembly 20 shown in FIGS.1 and 2. Referring to FIGS. 1, 2, and 3, the resistor assembly 20further comprises a plurality of vias 50 and a conductive path 52, wherethe conductive path 52 is part of the second layer 26 of the resistorassembly 20. Both the vias 50 and the conductive path 52 are constructedof a conductive alloy. The conductive path 52 is divided into a firstportion 52A and a second portion 52B, where the resistor assembly 20electrically couples the first portion 52A of the conductive path 52 tothe second portion 52B of the conductive path 52. Specifically, as seenin FIGS. 1 and 3, one of the plurality of vias 50A electrically couplesthe first portion 52A of the conductive path 52 to the second conductivetrace 42 of the surface mounted layer 24.

Referring specifically to FIG. 3, the embedded thin film resistor 28comprises a first section 60 and a second section 62. The first section60 of the embedded thin film resistor 28 is shaped to correspond with aprofile of the first conductive trace 40. For example, in the embodimentas shown, the first conductive trace 40 comprises an arcuate profile.Accordingly, the first section 60 of the embedded thin film resistor 28is shaped as an arcuate profile as well. The second section 62 of theembedded thin film resistor 28 comprises a linear profile. In theembodiment as shown in FIG. 3, the second section 62 of the embeddedthin film resistor 28 defines a first end 64 and a second end 66. Thefirst end 64 of the second section 62 of the embedded thin film resistor28 generally opposes but does not make electrical contact with an end 68of the first portion 52A of the conductive path 52. However, the secondend 66 of the second section 62 of the embedded thin film resistor 28 iselectrically coupled to the second portion 52B of the conductive path52. Specifically, in the embodiment as shown in FIG. 3, an electricaltrace 76 electrically couples the second end 66 of the second section 62of the embedded thin film resistor 28 with an end of the second portion52B of the conductive path 52.

The plurality of vias 50 electrically couple the first conductive trace40 of the surface mounted layer 24 to the embedded thin film resistor28. Specifically, the plurality of vias 50 electrically couple the firstconductive trace 40 of the surface mounted layer 24 to the secondsection 62 of the embedded thin film resistor 28. As mentioned above,the first conductive trace 40 is electrically coupled to the secondconductive trace 42 by the trimming bridges 44. Accordingly, as seen inFIG. 3, current C flows from the first portion 52A of the conductivepath 52 to the via 50A, and from the via 50A to the second conductivetrace 42. The current C then flows from the second conductive trace 42to the first conductive trace 40 though the trimming bridges 44, andfrom the first conductive trace 40 to the first section 60 of theembedded thin film resistor 28 by the vias 50. The current C then flowsthrough the thin film resistor 28 and to the second portion 52B of theconductive path 52 through the electrical trace 76.

FIG. 4A is a top view of the uppermost surface 30 of the multilayersubstrate 10, where the surface mounted layer 24 of the resistorassembly 20 comprises both the first conductive section 36 and thesecond conductive section 38. FIG. 4B is an alternative embodiment ofthe surface mounted layer 24 shown in FIG. 4B. FIG. 5 is an elevatedperspective view of the resistor assembly 20 shown in FIG. 4A. Referringto FIGS. 4A and 5, in the embodiment as shown, the trimming bridges 44of the first conductive section 36 are referred to as first trimmingbridges 144 and the vias 150 of the first conductive section 36 arereferred to as the first vias 150. The resistor assembly 20 furthercomprises a third conductive trace 70 and a second conductive trace 72that are electrically coupled to one another. Specifically, the thirdconductive trace 70 and the fourth conductive trace 72 are electricallycoupled to one another by a plurality of second trimming bridges 74. Thethird conductive trace 70 is electrically coupled to the embedded thinfilm resistor 28 by a plurality of second vias 80.

Referring to FIG. 4A, the fourth conductive trace 72 is positionedradially outward relative to the third conductive trace 70. The firstconductive trace and the second conductive trace are arrangedconcentrically with respect to one another. Similarly, the thirdconductive trace 70 and the fourth conductive trace 72 are arrangedconcentrically with respect to one another. The first conductive trace40, the second conductive trace 42, the third conductive trace 70, andthe fourth conductive trace 72 are each positioned radially outwardrelative to the common central axis 46. The first conductive trace 40,the second conductive trace 42, the third conductive trace 70 and thefourth conductive trace 72 each comprise an arcuate profile. Asmentioned above, the first conductive trace 40, the second conductivetrace 42, the third conductive trace 70 and the fourth conductive trace72 are not limited to the profile as shown in the figures.

Referring to FIG. 5, the second portion 52B of the conductive path 52 iselectrically coupled to the fourth conductive trace 72 by one of thesecond vias 80A. In the embodiment as shown in FIG. 5, the embedded thinfilm resistor 28 comprises the first section 60, the second section 62,and an additional third section 164. The first section 60 of theembedded thin film resistor 28 is shaped to substantially correspondwith a profile of the first conductive trace 40, the second section 62of the embedded thin film resistor 28 comprises a linear profile, andthe third section 164 of the embedded thin film resistor 28 is shaped tosubstantially correspond with a profile of the third conductive trace70.

Referring back to FIG. 4A, in the embodiment as shown the surfacemounted layer 24 defines an axis of symmetry A-A disposed along theuppermost surface 30 of the multilayer substrate 10. The axis ofsymmetry A-A positioned perpendicular with respect to the common centralaxis C-C. As seen in FIG. 4A, the profiles of the first conductive trace40 and the second conductive trace 42 are identical to the profiles ofthe third conductive trace 70 and the fourth conductive trace 72.Furthermore, as seen in FIG. 4A, the surface mounted layer 24 comprisesan equal number of first trimming bridges 144 and second trimmingbridges 74. Thus, the first conductive section 36 of the surface mountedlayer 24 is symmetrical with respect to the second conductive section 38of the surface mounted layer 24.

Although FIG. 4A illustrates a symmetrical surface mounted layer 24, itis to be appreciated that in another approach the surface mounted layer24 is not symmetrical. For example, in the embodiment as shown in FIG.4B, the surface mounted layer 24 comprises an unequal number of firsttrimming bridges 144 and second trimming bridges 74. Specifically, inthe example as shown, there are five first trimming bridges 144 butthree second trimming bridges 74. However, it is to be appreciated thatFIG. 4B is merely exemplary in nature, and the surface mounted layer 24may comprise other asymmetrical configurations as well. For example, inanother embodiment, the first conductive trace 40 and the secondconductive trace 42 comprises a profile that does not match the profileof the third conductive trace 70 and the fourth conductive trace 72. Inthe example as shown in FIG. 4B, the ends 190, 192 of the thirdconductive trace 70 and the ends 194, 196 the fourth conductive trace 72(shown in phantom line) are omitted.

FIGS. 6A-6E illustrate an exemplary process of removing the trimmingbridges 74, 144 to tune a resistance of the embedded thin film resistor28 (not shown in FIGS. 6A-6E). It is to be appreciated that as thetrimming bridges 74, 144 are removed, the resistance of the embeddedthin film resistor 28 increases. For example, FIG. 6A illustrates aninitial condition, where all of the first trimming bridges 144 and thesecond trimming bridges 74 are intact. Before any trimming bridges 74,144 are removed, the resistor assembly 20 has an initial resistance ofR+r0, where r0=0.

The individual first trimming bridges 144 are arranged as 144A, 144B,144C, 144D, 144E, where the first trimming bridge 144A is disposedbetween the end 180 of the first conductive trace 40 and the end 182 ofthe second conductive trace. The first trimming bridge 144E is disposedbetween the end 184 of the first conductive trace 40 and the end 186 ofthe second conductive trace 42. The first trimming bridges 144A, 144B,144C, 144D, 144E are arranged in chronological order. Accordingly, thefirst trimming bridge 144A is positioned directly adjacent to firsttrimming bridge 144B, first trimming bridge 144B is positioned directlyadjacent to first trimming bridge 144C, first trimming bridge 144C ispositioned directly adjacent to first trimming bridge 144D, and firsttrimming bridge 144D is positioned adjacent to first trimming bridge144E. Similarly, the individual second trimming bridges 74 are arrangedas 74A, 74B, 74C, 74D, 74E, where the second trimming bridge 74A isdisposed between the end 190 of the third conductive trace 70 and theend 192 of the fourth conductive trace 72. The second trimming bridge74E is disposed between the end 194 of the third conductive trace 70 andthe end 196 of the fourth conductive trace 72. The second trimmingbridges 74A, 74B, 74C, 74D, 74E are arranged in chronological order.

One or more trimming bridges 74, 144 are then removed to incrementallyincrease the resistance of the resistor assembly 20. For example,referring to FIG. 6B, one of the first trimming bridges 144 and one ofthe second trimming bridges 74 are removed. Specifically, the trimmingbridges 144A and 74A are removed using laser ablation. Accordingly, theresistance of the resistor assembly 20 is now R+r1, where r represents aresistance value that is created by the removal of trimming bridges 74Aand 144A. Similarly, as seen in FIG. 6C, the trimming bridges 74B and144B are removed using laser ablation. Since the surface mounted layer24 is symmetrical, r2 is twice the value of r1. Accordingly, theresistance of the resistor assembly 20 is now R+r2, where r2 is twicethe value of r1. Referring now to FIG. 6D, in an embodiment, thetrimming bridges 74C, 144C are removed using laser ablation, and theresistance of the resistor assembly 20 is now R+r3, where r3 is threetimes the value of r1. Finally, as seen in FIG. 6E, the trimming bridges74D, 144D are removed using laser ablation, and the resistance of theresistor assembly 20 is now R+r3, where r4 is four times the value ofr1.

The surface mounted layer 24 shown in FIGS. 6A-6E is symmetrical, andtherefore there is a linear increase in resistance are the trimmingbridges 74, 144 are removed. However, if the surface mounted layer 24 isasymmetrical, then the resistance simply increases in value (i.e.,r1<r2<r3<r4). Furthermore, it is to be appreciated that while laserablation is described, other methodologies may also be used to removethe trimming bridges 74, 144 as well. Some examples of other approachesto remove the trimming bridges 74, 144 include, but are not limited to,chemical etching or mechanical removal.

Referring generally to FIGS. 6A-6E, adjacent trimming bridges 74, 144are removed, which results in an incremental linear increase inresistance. Specifically, the first trimming bridge 144A and the secondtrimming bridge 74A are removed. Next, the first trimming bridge 144B isremoved, where the first trimming bridge 144B is positioned directlyadjacent to the first trimming bridge 144A. Moreover, the secondtrimming bridge 74B is removed, where the second trimming bridge 74B ispositioned directly adjacent to the second trimming bridge 74A.Accordingly, there is a linear increase in resistance of r1.

FIG. 7 is a schematic diagram of an exemplary four-point probe 200configured to probe the surface mounted layer 24 of the resistorassembly 20 (seen in FIGS. 6A-6E) and obtain resistance measurements.Specifically, the four-point probe 200 performs four-point sensing,which is also referred to as Kelvin sensing. The four-point probe 200comprises two insulated clips 201A, 201B. The insulated clip 201Acomprises two probes 202A, 204A, and the insulated clip 201B comprisesprobes 202B, 204B. The probes 202A, 202B are configured to measure acurrent and the probes 204A, 204B configured to measure voltage.

FIG. 8 is an illustration of the surface mounted layer 24 of theresistor assembly 20. A first probing location 206A is located on theend 182 of the second conductive trace 42 of the surface mounted layer24 and corresponds to the clip 201A. The four-point probe 200 measures afirst current measurement I₁ and a first voltage measurement V₁ at thefirst probing location 206A. A second probing location 206B is locatedon the end 196 of the third conductive trace 72 and corresponds to theclip 201B. the four-point probe 200 measures a second currentmeasurement 12 and a second voltage measurement V₂. The currentmeasurements I₁, I₂ and the voltage measurements V₁, V₂ are used todetermine the resistance of the resistor assembly 20.

FIG. 9 is an exemplary process flow diagram illustrating a method 300for tuning the resistance of the resistor assembly 20. Referringgenerally to FIGS. 5, 6A-6E, and 7-9, the method 300 begins at block302. In block 302, an initial resistance measurement of the resistorassembly 20 is obtained by probing the surface mounted layer 24 of theresistor assembly 20 by the four-point probe 200. Referring specificallyto FIG. 5, the surface mounted layer 24 of the resistor assembly 20 iselectrically coupled to the embedded thin film resistor 28 by a tuningpattern disposed along the surface mounted layer 24 of the resistorassembly 20. The tuning pattern comprises one or more pairs ofconductive traces (i.e., the conductive traces 40, 42 and the conductivetraces 70, 72), where each pair of conductive traces are electricallycoupled to one another by the plurality of trimming bridges 74, 144. Themethod 300 can then proceed to block 304.

In block 304, the initial resistance measurement is compared to adefined resistance criteria. The defined resistance criteria indicates aresistance range or, alternatively, a resistance threshold of theresistor assembly 20. For example, in one non-limiting embodiment, thepredefined resistance criteria is a resistance range that comprises of atolerance of two percent. The method 300 can then proceed to decisionblock 306.

In decision block 306, the method 300 can either proceed to block 308 orterminate. Specifically, if the initial resistance measurement satisfiesthe defined resistance criteria, then the method 300 can then terminate.However, in response to determining the initial resistance measurementdoes not satisfy the defined resistance criteria the method 300 can thenproceed to block 308.

In block 308, one or more trimming bridges 74, 144 that are part of thesurface mounted layer 24 are removed. For example, in the embodiment asshown in FIGS. 6A-6E, the surface mounted layer 24 comprises two pairsof conductive traces (40, 42, and 70, 72). Therefore, two trimmingbridges 74, 144 are removed at a time. However, in the embodiment asshown in FIGS. 2 and 3, the surface mounted layer 24 comprises only onepair of conductive traces 40, 42. Accordingly, one trimming bridge 44 isremoved at a time. As mentioned above, the trimming bridges 74, 144 areremoved using laser ablation. The method 300 can then proceed to block310.

In block 310, a subsequent resistance measurement of the resistorassembly 20 is obtained by probing the surface mounted layer 24 of theresistor assembly 20 by the four-point probe 200. The method 300 canthen proceed to block 312.

In block 312, the subsequent resistance measurement of the resistorassembly 20 is compared to the defined resistance criteria. The method300 can then proceed to decision block 314.

In decision block 314, the method 300 can either proceed to block 308 orterminate. Specifically, if the subsequent resistance measurementsatisfies the defined resistance criteria, then the method 300 can thenterminate. However, in response to determining the subsequent resistancemeasurement does not satisfy the defined resistance criteria the method300 can then proceed to block 316.

In block 316, one or more subsequent trimming bridges 74, 144 that arepart of the surface mounted layer 24 are removed. For example, the oneor more subsequent trimming bridges 74, 144 are shown in FIG. 6C astrimming bridges 74B, 144B. In the embodiment as shown in FIG. 6D, theone or more subsequent trimming bridges 74, 144 are shown as 74C, 144C.In the embodiment as shown in FIG. 6E, the one or more subsequenttrimming bridges 74, 144 are shown as 74D, 144D. The method 300 can thenreturn to block 310 to obtain another subsequent resistance measurement.

FIG. 10 illustrates an alternative embodiment of a resistor assembly 20comprising a thin film resistor 428. As seen in FIG. 10, the thin filmresistor 428 is not embedded within the multilayer substrate 10.Instead, the thin film resistor 428 is part of the surface mounted layer24. In other words, the thin film resistor 428 is disposed along theuppermost surface 30 of the multilayer substrate 10 (FIG. 1). However,it is to be appreciated that surface mounting the thin film resistor 428requires more area along the uppermost surface 30 of the multilayersubstrate 10 when compared to the embedded thin film resistor 28.Similar to the embodiment as shown in FIG. 5, the first conductive trace40 is electrically coupled to the second conductive trace 42 by theplurality of first trimming bridges 144, and the third conductive trace70 is electrically coupled to the fourth conductive trace 72 by theplurality of second trimming bridges 74.

The thin film resistor 428 is electrically coupled to the firstconductive trace 40 by an electrical trace 450. Specifically, the thinfilm resistor 428 defines a first end 460 and a second end 462, wherethe first end 460 of the thin film resistor 428 is electrically coupledto the first conductive trace 40 by the electrical trace 450. The thinfilm resistor 428 is electrically coupled to the third conductive trace70 by an electrical trace 452. Specifically, the second end 462 of thethin film resistor 428 is electrically coupled to the third conductivetrace 70 by the electrical trace 452. Both electrical traces 450, 452are conductive lines or, alternatively, solder drops.

The second conductive trace 42 is electrically coupled to the firstportion 52A of the conductive path 52 by an electrical trace 456.Similarly, the fourth conductive trace 72 is electrically coupled to thesecond portion 52B of the conductive path 52 by an electrical trace 458.The electrical traces 450, 452, 456, and 458 are all part of the surfacemounted layer 24 of the resistor assembly 20.

Referring generally to the figures, the present disclosure offersvarious technical effects and benefits. Specifically, the resistance ofthe thin film resistor is fine-tuned by incrementally removing thetrimming bridges to achieve a defined resistance criterion. Accordingly,the disclosure provides a system and method for fine-tuning theresistance of the thin film resistor that is independent of theprocesses used to fabricate the thin film resistor and the multilayersubstrate. The disclosed approach for fine-tuning a thin film resistoris especially advantageous, since it may be relatively difficult tocontrol the fabrication processes used to create the thin film resistorand the corresponding multilayer substrate.

Further, the disclosure comprises embodiments according to the followingclauses:

Clause 1: a resistor assembly, comprising: a first conductive trace, asecond conductive trace, and a plurality of trimming bridges thatelectrically couple the first conductive trace to the second conductivetrace; and a thin film resistor electrically coupled to the firstconductive trace, wherein the first conductive trace, the secondconductive trace, the plurality of trimming bridges, and the thin filmresistor are all part of a surface mounted layer of the resistorassembly, and wherein the plurality of trimming bridges are eachremovable to increase a resistance of the thin film resistor.

Clause 2: the resistor assembly of clause 1, further comprising anelectrical trace that is part of the surface mounted layer, wherein theelectrical trace electrically couples the thin film resistor to thefirst conductive trace.

Clause 3: the resistor assembly of any of clauses 1 or 2, wherein theplurality of trimming bridges are spaced at equal distances from oneanother, and wherein spacing the plurality of trimming bridges at equaldistances from one another results in a linear increase in theresistance of the thin film resistor as each trimming bridge is removed.

Clause 4: the resistor assembly of any of clauses 1, 2, or 3, whereinthe first conductive trace and the second conductive trace are arrangedconcentrically with respect to one another.

Clause 5: the resistor assembly of any of clauses 1, 2, 3, or 4, whereinthe first conductive trace and the second conductive trace both comprisean arcuate profile.

Clause 6: the resistor assembly of any of clauses 1, 2, 3, 4, or 5,wherein the plurality of trimming bridges are first trimming bridges,and wherein the surface mounted layer further comprises: a thirdconductive trace and a fourth conductive trace electrically coupled toone another, wherein the third conductive trace is electrically coupledto the thin film resistor.

Clause 7: the resistor assembly of any of clauses 1, 2, 3, 4, 5, or 6,further comprising an electrical trace that is part of the surfacemounted layer, wherein the electrical trace electrically couples thethin film resistor to the third conductive trace.

Clause 8: the resistor assembly of any of clauses 1, 2, 3, 4, 5, 6, or7, wherein the third conductive trace and the fourth conductive traceare electrically coupled to one another by a plurality of secondtrimming bridges.

Clause 9: the resistor assembly of any of clauses 1, 2, 3, 4, 5, 6, 7,or 8, wherein the first conductive trace and the second conductive traceare arranged concentrically with respect to one another, and the thirdconductive trace and the fourth conductive trace are arrangedconcentrically with respect to one another.

Clause 10: the resistor assembly of any of clauses 1, 2, 3, 4, 5, 6, 7,8, or 9, wherein first conductive trace, the second conductive trace,the third conductive trace, and the fourth conductive trace eachcomprise an arcuate profile.

Clause 11: the resistor assembly of any of clauses 1, 2, 3, 4, 5, 6, 7,8, 9, or 10, wherein the surface mounted layer comprises an equal numberof first trimming bridges and second trimming bridges.

Clause 12: the resistor assembly of any of clauses 1, 2, 3, 4, 5, 6, 7,8, 9, 10, or 11, wherein the surface mounted layer further comprises afirst electrical trace and a conductive path, wherein the firstelectrical trace electrically couples a first portion of the conductivepath to the second conductive trace.

Clause 13: the resistor assembly of any of clauses 1, 2, 3, 4, 5, 6, 7,8, 9, 10, 11, or 12, wherein a second portion of the conductive path iselectrically coupled to the thin film resistor by a second electricaltrace.

Clause 14: a multilayer substrate, comprising: an uppermost layerdefining an uppermost surface of the multilayer substrate; and aresistor assembly comprising a surface mounted layer disposed along theuppermost layer of the of the multilayer substrate, the surface mountedlayer of the resistor assembly comprising: a first conductive trace, asecond conductive trace, and a plurality of trimming bridges thatelectrically couple the first conductive trace to the second conductivetrace; and a thin film resistor electrically coupled to the firstconductive trace, wherein the plurality of trimming bridges are eachremovable to increase a resistance of the thin film resistor.

Clause 15: the multilayer substrate of clause 14, wherein the pluralityof trimming bridges are spaced at equal distances from one another, andwherein spacing the trimming bridges at equal distances from one anotherresults in a linear increase in the resistance of the thin film resistoras each trimming bridge is removed.

Clause 16: the multilayer substrate of clause 14 or 15, wherein theplurality of trimming bridges are first trimming bridges, and whereinthe surface mounted layer further comprises: a third conductive traceand a fourth conductive trace electrically coupled to one another,wherein the third conductive trace is electrically coupled to the thinfilm resistor.

Clause 17: the multilayer substrate of clause 14, 15, or 16, wherein thethird conductive trace and the fourth conductive trace are electricallycoupled to one another by a plurality of second trimming bridges.

Clause 18: a system for determining resistance, comprising: a resistorassembly comprising a surface mounted layer, the surface mounted layerof the resistor assembly comprising: a first conductive trace, a secondconductive trace, and a plurality of first trimming bridges thatelectrically couple the first conductive trace to the second conductivetrace; a third conductive trace, a fourth conductive trace, and aplurality of second trimming bridges that electrically couple the thirdconductive trace to the fourth conductive trace; a thin film resistorelectrically coupled to the first conductive trace and the thirdconductive trace, wherein the plurality of first trimming bridges andthe plurality of second trimming bridges are each removable to increasea resistance of the thin film resistor; and a first probing locationdisposed on the second conductive trace and a second probing locationdisposed on the third conductive trace; and a probe configured tomeasure a first current measurement and a first voltage measurement atthe first probing location and a second current measurement and a secondvoltage measurement at the second probing location, wherein the firstcurrent measurement, the first voltage measurement, the second currentmeasurement, and the second voltage measurement determine the resistanceof the resistor assembly.

Clause 19: the system of clause 18, wherein the probe is a four-pointprobe configured to probe the surface mounted layer of the resistorassembly, and wherein the four-point probe comprises two insulatedclips.

Clause 20: the system of any of clauses 18 or 19, wherein one of the twoinsulated clips measures the first current measurement and the firstvoltage measurement at the first probing location and a remaining one ofthe two insulated clips measures the second current measurement and thesecond voltage measurement at the second probing location.

The description of the present disclosure is merely exemplary in natureand variations that do not depart from the gist of the presentdisclosure are intended to be within the scope of the presentdisclosure. Such variations are not to be regarded as a departure fromthe spirit and scope of the present disclosure.

What is claimed is:
 1. A resistor assembly, comprising: a firstconductive trace, a second conductive trace, and a plurality of trimmingbridges that electrically couple the first conductive trace to thesecond conductive trace; and a thin film resistor electrically coupledto the first conductive trace, wherein the first conductive trace, thesecond conductive trace, the plurality of trimming bridges, and the thinfilm resistor are all part of a surface mounted layer of the resistorassembly, and wherein the plurality of trimming bridges are eachremovable to increase a resistance of the thin film resistor.
 2. Theresistor assembly of claim 1, further comprising an electrical tracethat is part of the surface mounted layer, wherein the electrical traceelectrically couples the thin film resistor to the first conductivetrace.
 3. The resistor assembly of claim 1, wherein the plurality oftrimming bridges are spaced at equal distances from one another, andwherein spacing the plurality of trimming bridges at equal distancesfrom one another results in a linear increase in the resistance of thethin film resistor as each trimming bridge is removed.
 4. The resistorassembly of claim 1, wherein the first conductive trace and the secondconductive trace are arranged concentrically with respect to oneanother.
 5. The resistor assembly of claim 4, wherein the firstconductive trace and the second conductive trace both comprise anarcuate profile.
 6. The resistor assembly of claim 1, wherein theplurality of trimming bridges are first trimming bridges, and whereinthe surface mounted layer further comprises: a third conductive traceand a fourth conductive trace electrically coupled to one another,wherein the third conductive trace is electrically coupled to the thinfilm resistor.
 7. The resistor assembly of claim 6, further comprisingan electrical trace that is part of the surface mounted layer, whereinthe electrical trace electrically couples the thin film resistor to thethird conductive trace.
 8. The resistor assembly of claim 6, wherein thethird conductive trace and the fourth conductive trace are electricallycoupled to one another by a plurality of second trimming bridges.
 9. Theresistor assembly of claim 8, wherein the first conductive trace and thesecond conductive trace are arranged concentrically with respect to oneanother, and the third conductive trace and the fourth conductive traceare arranged concentrically with respect to one another.
 10. Theresistor assembly of claim 9, wherein the first conductive trace, thesecond conductive trace, the third conductive trace, and the fourthconductive trace each comprise an arcuate profile.
 11. The resistorassembly of claim 8, wherein the surface mounted layer comprises anequal number of first trimming bridges and second trimming bridges. 12.The resistor assembly of claim 6, wherein the surface mounted layerfurther comprises a first electrical trace and a conductive path,wherein the first electrical trace electrically couples a first portionof the conductive path to the second conductive trace.
 13. The resistorassembly of claim 12, wherein a second portion of the conductive path iselectrically coupled to the thin film resistor by a second electricaltrace.
 14. A multilayer substrate, comprising: an uppermost layerdefining an uppermost surface of the multilayer substrate; and aresistor assembly comprising a surface mounted layer disposed along theuppermost layer of the of the multilayer substrate, the surface mountedlayer of the resistor assembly comprising: a first conductive trace, asecond conductive trace, and a plurality of trimming bridges thatelectrically couple the first conductive trace to the second conductivetrace; and a thin film resistor electrically coupled to the firstconductive trace, wherein the plurality of trimming bridges are eachremovable to increase a resistance of the thin film resistor.
 15. Themultilayer substrate of claim 14, wherein the plurality of trimmingbridges are spaced at equal distances from one another, and whereinspacing the trimming bridges at equal distances from one another resultsin a linear increase in the resistance of the thin film resistor as eachtrimming bridge is removed.
 16. The multilayer substrate of claim 14,wherein the plurality of trimming bridges are first trimming bridges,and wherein the surface mounted layer further comprises: a thirdconductive trace and a fourth conductive trace electrically coupled toone another, wherein the third conductive trace is electrically coupledto the thin film resistor.
 17. The multilayer substrate of claim 16,wherein the third conductive trace and the fourth conductive trace areelectrically coupled to one another by a plurality of second trimmingbridges.
 18. A system for determining resistance, comprising: a resistorassembly comprising a surface mounted layer, the surface mounted layerof the resistor assembly comprising: a first conductive trace, a secondconductive trace, and a plurality of first trimming bridges thatelectrically couple the first conductive trace to the second conductivetrace; a third conductive trace, a fourth conductive trace, and aplurality of second trimming bridges that electrically couple the thirdconductive trace to the fourth conductive trace; a thin film resistorelectrically coupled to the first conductive trace and the thirdconductive trace, wherein the plurality of first trimming bridges andthe plurality of second trimming bridges are each removable to increasea resistance of the thin film resistor; and a first probing locationdisposed on the second conductive trace and a second probing locationdisposed on the third conductive trace; and a probe configured tomeasure a first current measurement and a first voltage measurement atthe first probing location and a second current measurement and a secondvoltage measurement at the second probing location, wherein the firstcurrent measurement, the first voltage measurement, the second currentmeasurement, and the second voltage measurement determine the resistanceof the resistor assembly.
 19. The system of claim 18, wherein the probeis a four-point probe configured to probe the surface mounted layer ofthe resistor assembly, and wherein the four-point probe comprises twoinsulated clips.
 20. The system of claim 19, wherein one of the twoinsulated clips measures the first current measurement and the firstvoltage measurement at the first probing location, and wherein aremaining one of the two insulated clips measures the second currentmeasurement and the second voltage measurement at the second probinglocation.